Fluid machine

ABSTRACT

A fluid machine for compressing or conveying fluids, in particular for compressing gases to high pressures, has a linear motor ( 2 ), at least one cylinder ( 3 ), a solid or liquid piston ( 4, 4 ′) which can be moved axially in the cylinder ( 3 ), and at least one compression space ( 5 ) which is formed between the cylinder ( 3 ) and the solid or liquid piston ( 4, 4 ′), wherein the linear motor ( 2 ) applies translational driving force to the solid or liquid piston ( 4, 4 ′). For such a fluid machine, the leakage-free and lubricant-free compression and conveying of fluids, in particular a compression of gases to high pressures, and a rather simple construction is made possible owing to the fact that the solid or liquid piston ( 4, 4 ′) is surrounded in the area of the linear motor ( 2 ) by a firmly attached pipe section ( 6 ).

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a fluid machine for compressing or conveyingfluids, especially for compressing gases to high pressures, with alinear motor, at least one cylinder, a solid piston which can be movedaxially in the cylinder, or an axially movable liquid piston and atleast one compression space which is made between the cylinder and thesolid piston and the liquid piston, the linear motor transferring atranslational driving force to the solid piston or the liquid piston.

2. Description of Related Art

Fluid machines are known in the prior art in different embodiments andversions. Fluid machines can be subdivided, first of all, according towhether they are intended for conveying or compressing liquids or gases.Fluid machines which are used for conveyance of liquids are generallyalso called pumps, while fluid machines for compressing gases are calledcompressors. Moreover fluid machines can also be distinguished dependingon the type of driving force—hydraulic, electrical or electromagnetic,and according to the type of driving motion—rotational or translational.

This invention relates to a fluid machine in which the driving force isproduced by a linear motor which applies a translational driving forcedirectly to the piston which is guided in the cylinder, i.e., withoutconversion of rotary motion by way of gearing. If a gas is to becompressed with such a fluid machine, the machine can also be called apiston compressor or linear compressor. The linear motor here isessentially comprised of a stator and a rotor or actuator, and thelinear motor as well as the synchronous motor can also be made as anasynchronous or synchronous linear motor. The linear motor thencorresponds to an unwound asynchronous motor with a squirrel cage rotoror a permanently excited synchronous motor, a travelling field beingproduced by the coil or winding of the stator instead of a rotatingfield. Force is transferred as in a polyphase machine, either by voltageinduction in a squirrel cage rotor of the asynchronous motor or byinteraction with the field of the permanent magnets of the synchronousmotor.

German Patent Application DE 10 2004 055 924 A1 discloses a linearcompressor which has been described before, in which the magnet of therotor is fastened to a magnet frame which is securely attached to oneface side of the piston. In the known linear compressor, to cool thelinear motor there is a cooling channel by which the coil of the statorattached to the coil holder is cooled with a coolant. To do this thereis a pump which conveys oil within the receptacle which hermeticallyseals the linear compressor through the cooling channel to the coil orto the coil holder. The returning oil is collected in the lower part ofthe hermetically sealed receptacle.

German Patent Application DE 102 14 047 A1 discloses a compressor for amotor vehicle air conditioning system with a closed coolant circuitwhich has a compressor housing with a compression space made in it and ajacking piston which can move back and forth in it and in which thedrive for the compressor is a linear motor with a variable triggerfrequency, to whose reaction part the jacking piston is attached on thecompressor space-side end face of the jacking piston. The knowncompressor is of simple structure, consists of only a few parts and isrelatively small. Bearing, lubrication and sealing problems do notarise, in any case at a pressure level on the high pressure side between80 and 160 bar. The sealing of the jacking piston relative to thecompression space wall is effected by means of conventional ring sealson the jacking piston. Since, for these movable seals, leakages to theatmosphere in principle occur at least over time, the compressor knownfrom German Patent Application DE 102 14 047 A1 is not suitable at leastfor sealing high pressures (>150 bar) and is not intended for thispurpose either.

It was stated initially that the fluid machine has a solid piston whichcan be moved axially in a cylinder, or an axially movable liquid piston.A solid piston within the framework of the invention is defined as a(conventional) solid (metal) piston, as has been known for a long time.The above described compressors have these solid pistons. A liquidpiston, conversely, within the framework of the invention, is defined asa liquid which is indeed liquid, but behaves like a solid whencompression of the gas is achieved by changing the liquid level. Here,the liquid and the gas to be compressed are both in the cylinder,without however the liquid and gas mixing. The liquid piston thusassumes the function of a solid piston, the liquid piston as well as thesolid piston being translationally driven by the travelling magneticfield of the linear motor which has been produced by means of coils.

A fluid machine with a liquid piston is known for example from GermanPatent Application DE 10 2004 046 316 A1 and corresponding U.S. PatentApplication Publication 2007/0258828 A1. In the compressor disclosedthere, preferably, an ionic liquid being used so that the compressor isalso called an “ionic compressor”. The known compressor has twocylinders which are connected to one another and in which one liquid andone gas to be compressed at a time are located. By means of a hydraulicpump the liquid levels in the two cylinders are varied such that one ofthe cylinders intakes the gas which is to be compressed, whilecompression of the gas occurs in the other cylinder.

SUMMARY OF THE INVENTION

The object of this invention is to provide the initially described fluidmachine for compression or conveyance of fluids with a structure that isas simple as possible and enables leak-free and as much as possible alsolubricant-free compression or conveyance of fluids, especiallycompression of gases to high pressures.

This object is achieved in the initially described fluid machine, firstof all, in that the solid piston or liquid piston in the region of thelinear motor is surrounded by a permanently arranged split pipe.Prevention of leakage to the atmosphere can be easily achieved by thearrangement of a split pipe. The leaks which occur on moving seals asdictated by principle when the solid piston is sealed to the drive, andthus, to the atmosphere are prevented by the split pipe. Sealing to theatmosphere can be achieved by the arrangement of the split pipe solelywith static seals.

First of all, preferred embodiments of a fluid machine with a solidpiston, i.e., with a massive piston, are described below. According to afirst advantageous configuration of the invention, the split pipe in theradial direction is located between the rotor and the coil of the statorso that the split pipe surrounds the rotor. In this embodiment, thesplit pipe is located between the stator and the rotor. According to onealternative configuration of the invention, both the rotor and also thecoil of the stator are located within the split pipe so that the splitpipe surrounds the rotor and the stator.

In the first embodiment, the split pipe is thus used as a partitionbetween the electrical drive system and the compression space in contactwith the fluid and the moving solid piston, the split pipe beingpenetrated by a magnetic field for energy transmission. In this way,electrical losses as a result of eddy currents occur in the split pipeand the split pipe is heated so that the efficiency of the linear motorwith the split-pipe located in between is less than the efficiency of alinear motor with a split pipe which lies outside. This disadvantage ofgreater losses does not occur in the second embodiment in which thesplit-pipe surrounds the rotor and the stator. This embodiment is atleast theoretically advantageous unless corrosive media are to becompressed with the fluid machine. In this case, the coil for an outsidesplit pipe would likewise be exposed to a corrosive medium; this canlead to an adverse effect on the service life of the coil.

The fluid machine in accordance with the invention can advantageously beeasily built by the magnets of the rotor being located directly on thepiston. Attaching the magnets of the rotor directly to the pistoneliminates the need to make and arrange a separate magnet frame.Moreover, the radial dimensions of the fluid machine, especially of thecylinder, can be reduced by this configuration.

According to another preferred embodiment of the invention, the fluidmachine is made in several stages, i.e., compression of the gas takesplace in at least two, preferably in four stages. Alternativelysingle-stage compression is also possible, then preferably there beingone equalization stage to keep the resulting forces necessary forcompression low. If compression of the gas takes place in severalstages, it is more advantageously provided that the solid piston hasseveral sections with different diameters. The piston can be composed ofseveral piston sections in terms of production engineering.

According to another advantageous configuration of the fluid machine inaccordance with the invention with a solid piston, the compression spaceconnected to the split pipe is connected to the fluid entry side, i.e.,to the intake side of the fluid machine, directly or by way of a line ora channel made in the cylinder or in the housing. This measure reducesthe pressure in the region of the split pipe to a low pressure on thefluid entry side. Internal leaks which occur along the moving pistonseals are relieved to the intake pressure and discharged to the fluidentry side. In this way, the required wall thickness of the split pipecan be reduced, by which, in an arrangement of the split pipe betweenthe rotor and the coil of the stators, electrical losses are reduced. Athick-walled or double-walled execution of the split pipe which isotherwise necessary at especially high pressures can thus be eliminated,But regardless, a double-walled split pipe can be used to increasesafety, especially for dangerous gases (toxic, polluting, or radioactivegases.

To reduce electrical losses which can occur by using the split pipe, itis moreover possible to produce the split pipe from plastic or ceramic,not metal. In choosing the plastic or the ceramic, it must be noted thatthe split pipe can also reliably withstand the maximum pressure whichoccurs.

According to another configuration of the invention, as is fundamentallyknown in the prior art, there is at least one heat exchanger forre-cooling the fluid. In a multistage fluid machine, preferably, thereis one such heat exchanger after each compression stage. The coolantrequired for re-cooling the gas by the heat exchanger can thenpreferably also be used for cooling the linear motor. Cooling takesplace preferably from the outside, i.e., by way of the housing whichsurrounds the linear motor, so that neither the rotor nor the statorcomes into direct contact with the coolant. Alternatively to using aseparate coolant, both for re-cooling the fluid and also for cooling thelinear motor the fluid itself can be used if it is in thecorrespondingly cold state. If it is a gas which is to be compressed,for example hydrogen, which is supercold in the liquid phase beforecompression, the gas can be used as a coolant in the liquid phase.

In a fluid machine for compressing gases to high pressures with a liquidpiston the latter is preferably formed by a magnetizable liquid whichdoes not have a vapor pressure so that molecules of the liquid do notmix with the gas to be compressed. The liquid for this liquid piston canbe for example an ionic liquid. If such a liquid is used which does notmix with the gas to be compressed, as long as its decompositiontemperature is not reached, subsequent separation of the liquid from thegas which is being compressed can be omitted.

In a fluid machine with a liquid piston, the split pipe is located inthe radial direction preferably within the coil of the stator so thatthe split pipe surrounds the liquid which is acting as a rotor. In theregion of the linear motor, the split pipe thus has the function of thecylinder wall.

By using a liquid piston instead of a solid piston, not only the use ofa solid piston, but also the otherwise necessary piston seals, can beomitted. Sealing of the compression space takes place directly by theliquid which forms the liquid piston so that leakage to the atmospherecannot occur. Moreover, by eliminating the piston seals, the maintenancecost of the fluid machine is also reduced since there are no wearingparts within the working space.

In contrast to the “ionic compressor” known from the prior art, in thefluid machine in accordance with the invention, the liquid level ischanged, not by means of a hydraulic pump, but by a linear motor whosetravelling magnetic field, which is produced by the coils, applies atranslational motive force to the magnetizable liquid. By using a linearmotor instead of a hydraulic pump, on the one hand, a higher maximumpressure of the gas to be compressed can be achieved, and on the otherhand, the wear which occurs when using a hydraulic pump is avoided.

The use of a liquid piston also has the advantage that, by way of theliquid, at least partial discharge of the heat of compression whichforms during compression, and at the same time, cooling of the linearmotor, especially cooling of the coil of the stator, can take place. Forthis purpose, preferably, at least one heat exchanger is designed forre-cooling the liquid.

The above described fluid machine in accordance with the invention isespecially suited for compressing gases to high pressures, especiallyfor compression of hydrogen to 500 bar or more. Thus, such a linearcompressor is especially suited for outfitting hydrogen fillingstations.

In particular, there are a host of possibilities for embodying anddeveloping the fluid machine in accordance with the invention as will beapparent from the following description of preferred embodiments inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment of a fluid machine in accordance withthe invention,

FIG. 2 is an enlarged view of the encircled region A of the fluidmachine as shown in FIG. 1,

FIG. 3 shows a second embodiment of a fluid machine in accordance withthe invention,

FIG. 4 is an enlarged view corresponding to that of FIG. 2, but of thecorresponding region of the fluid machine as shown in FIG. 3,

FIG. 5 shows a third embodiment of a fluid machine in accordance withthe invention, and

FIG. 6 shows a fourth embodiment of a fluid machine in accordance withthe invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1, 3, 5 and 6 show four different embodiments of a fluid machine 1in accordance with the invention, the figures being solely simplifiedrepresentations, so that only the components important to the inventionare shown. The fluid machines 1 shown in the figures are used forcompressing gases, especially hydrogen, to a high pressure of 500 bar,for example. These fluid machines 1 can therefore advantageously be usedespecially for outfitting hydrogen filling stations.

The fluid machines 1 shown in FIGS. 1, 3, and 5 each have a linear motor2 for driving a solid piston 4 which is movably located in a cylinder 3.By using the linear motor 2 as a drive, a translational driving force isapplied to the solid piston 4 so that the solid piston 4 can move backand forth axially within the cylinder 3, 3′. Within the cylinder 3 is atleast one compression space 5 for the gas to be compressed, the size ofthe compression space changing depending on the position of the solidpiston 4.

In the two embodiments as shown in FIGS. 1 and 3, the fluid machine 1 ismade altogether in 4 stages, so that compression of the gas takes placein four succeeding stages. Accordingly, in these two embodiments, eachof the four sections 41, 42, 43, 44, of the solid piston 4 has adifferent diameter. Corresponding thereto, the cylinder 3, 3′ also hasfour different sections with different inside diameters so thataltogether four compression spaces 5 are formed. In contrast, the fluidmachine 1 as shown in FIG. 5 is made only with one stage, being adouble-acting fluid machine 1 so that one compression space 5 is formedon each of the two sides of the solid piston 4.

It is common to all three versions that the solid piston 4 is surroundedby a fixed split pipe 6 in the region of the linear motor 2. Thearrangement of the split pipe 6 ensures reliable sealing of the cylinderinterior 7 so that, altogether, the desired absence of leakage of thefluid machine 1 is easily achieved. The absence of leakage to theatmosphere need no longer be implemented by the piston seals 8 which arelocated on the solid piston 4 and which fundamentally cannot ensure theabsence of leakage due to their arrangement and execution as movingseals or cannot permanently do so and especially not without lubricant.The otherwise conventional execution of the piston rod to the drive isthus eliminated, likewise, the moving sealing systems required for thispurpose. The absence of leakage to the atmosphere is then ensuredexclusively with static seals 18.

The linear motor 2 shown in FIGS. 1 to 5 has a stator with a coil 9 anda rotor with several magnets 10, the magnets 10 being located directlyon the solid piston 4.

In the embodiment as shown in FIG. 1, or according to the enlargement inFIG. 2, the split pipe 6, in the radial direction, is located betweenthe rotor, i.e., the magnet 10 and the coil 9 of the stator, so that thesplit pipe 6 surrounds not only the solid piston 4, but also the magnets10 of the rotor. In this embodiment, the split pipe 6 is thus locatedbetween the stator and the rotor so that the split pipe 6 is penetratedby the magnetic field. In contrast thereto, in the embodiment as shownin FIG. 3 or according to the enlargement in FIG. 4, both the rotor,i.e., the magnet 10 and also the coil 9 of the stator, are locatedwithin the split pipe 6. In this embodiment thus not only the magnets10, but also the coil 9 is exposed to the fluid which in spite of thepiston seal 8 enters the cylinder interior 7 in the region of the splitpipe 6.

FIGS. 1, 3 and 5 indicate that the compression space 5, connected to thegap space 6, is connected by way of a line 11 to the fluid entry side 12of the fluid machine 1. This leads to internal leaks which occur inspite of the piston seals 8 between the outer periphery of the solidpiston 4 and the inside wall of the cylinder 3 being relieved to theintake pressure and discharged to the fluid entry side 12. In this way,the pressure in the cylinder interior 7 surrounded by the split pipe 6is reduced, by which the split pipe 6 in the configuration as shown inFIGS. 1 & 2 and the coil 9 and the split pipe 6 in the embodiment asshown in FIGS. 3 & 4 are not unnecessarily loaded. By the reduction ofpressure which has taken place in this way in the cylinder interior 7surrounded by the split pipe 6, a correspondingly smaller wall thicknessfor the split pipe 6 can be chosen, by which the eddy current losseswhich occur in the split pipe 6 are reduced.

Alternatively, the compression space 5 which is connected to the gapspace 6 can also be directly connected to the fluid entry side 12, i.e.,the fluid enters in the compression space 5 which is connected to thegap space 6. If the fluid to be compressed has a low temperature, thelinear motor 2 can thus be cooled at the same time.

As known in the prior art, inlet and outlet of the gas to be compressedtake place by way of valves 13 which are located in the region of theindividual compression space 5 and are preferably made as plate (leafspring) valves. Then, automatic opening and closing of the valves 13take place by the prevailing differential pressures between thecompression space 5 and the respective inlet and outlet. Since for thetwo embodiments as shown in FIGS. 1 & 3, four-stage compression of thegas takes place, the fluid machines 1 each also have four inlet andoutlet valves 13.

FIGS. 1 & 3, moreover, show that the individual compression spaces 5 areconnected to one another by way of lines 14, in the individual lines 14there being a respective heat exchanger 15 for re-cooling of thecompressed gas. Also, FIGS. 1, 3 and 5 show that the fluid machine 1,altogether, has a coolant circuit 16 for cooling the coil 9 of thestator and thus for cooling of the linear motor 2. Cooling takes placehere from the outside, i.e., by way of a housing 17 which surrounds thecoil 9, so that the coil does not come directly into contact with thecoolant. The same coolant can be used both for re-cooling the compressedgas in the heat exchangers 15 and also for cooling the linear motor 2.

Finally it is apparent from the figures that the illustrated embodimentsof the fluid machine 1 each have two cylinders 3, 3′, the linear motor 2with the split pipe 6 and the housing 17 surrounding the linear motor 2being located between the two cylinders 3, 3′. Sealing between the facesides of the two cylinders 3, 3′ and the corresponding face sides of thehousing 17 takes place by way of static seals 18.

FIGS. 3 & 4, moreover, show that the electric lines 19 to the statorlocated within the split pipe 6 are routed using pressure-tight cablepenetrations 20 without leaks to the terminal box 21, the terminal box21 also having pressure-tight cable penetrations 20 so that the absenceof leaks to the atmosphere which is obtained by the split pipe 6 is notneutralized by the connection of the necessary lines 19.

FIG. 6 shows an embodiment of a fluid machine 1 which, instead of asolid piston, has a liquid piston 4′. The liquid which forms the liquidpiston 4′ is located within the U-shaped housing which is formed fromthe two cylinders 3, 3′ and the split pipe 6. Above the liquid, in thetwo cylinders 3, 3′, there is a compression space 5 at each end of theliquid piston 4′ for the gas to be compressed, the size of the twocompression spaces 5 changing depending on the level of the liquid,i.e., on the position of the liquid piston 4′. The fluid machine 1 shownin FIG. 6, like the fluid machine 1 as shown in FIG. 5, is made with onestage, here its being a double acting fluid machine 1 so that on bothsides of the liquid piston 4′ a compression space 5 at a time is formed.

In each of the two compression spaces 5, there is a respective valve 13at the inlet and at the outlet, the outlets of the two compressionspaces 5 being connected to one another by way of lines 14 in which arespective heat exchanger 15 is located for re-cooling of the compressedgas. The linear motor 2 together with the split pipe 6 and the housing17 which surrounds the linear motor 2 is located between the twocylinders 3, 3′ so that the split pipe 6 constitutes the cylinder wallfor the liquid in the region of the linear motor 2.

The fluid machines 1 shown in the figures are especially suited forcompression of gases, preferably of hydrogen, to high pressures of, forexample, 1000 bar, so that these fluid machines 1 are especially wellsuited to outfitting of hydrogen filling stations.

1-16. (canceled)
 17. Fluid machine for compressing or conveying fluidsto high pressures, comprising at least one cylinder, a piston which ismovable axially in the cylinder, at least one compression space betweenthe cylinder and the piston, a linear motor, the linear motor apply atranslational driving force to the piston, wherein the piston issurrounded in a region of the linear motor by a permanently arrangedsplit pipe.
 18. Fluid machine as claimed in claim 17, wherein the pistonis a solid piston, wherein the linear motor has a stationary coil and atleast one movable magnet connected with the piston, and wherein thesplit pipe is located between the magnet and the coil in a radialdirection so that the split pipe surrounds the magnet.
 19. Fluid machineas claimed in claim 18, wherein the at least one magnet is locateddirectly on the piston.
 20. Fluid machine as claimed in claim 17,wherein the piston is a solid piston, wherein the linear motor has astationary coil and at least one movable magnet connected with thepiston, and wherein the split pipe surrounds both the coil and themagnet.
 21. Fluid machine as claimed in claim 20, wherein the at leastone magnet is located directly on the piston.
 22. Fluid machine asclaimed in claim 17, wherein the piston is a multi-stage, solid pistonfor compressing a gas in several stages.
 23. Fluid machine as claimed inclaim 22, wherein the solid piston has several sections of differentdiameters.
 24. Fluid machine as claimed in claim 17, wherein the pistonis a solid piston, wherein a fluid inlet side of the compression spaceis connected to the split pipe.
 25. Fluid machine as claimed in claim17, wherein the piston is a solid piston, and wherein a cooling circuitis provided for cooling the linear motor.
 26. Fluid machine as claimedin claim 17, wherein the piston is a solid piston and wherein at leastone heat exchanger is provided for re-cooling the fluid acted upon bythe piston.
 27. Fluid machine as claimed in claim 25, wherein at leastone heat exchanger is provided for re-cooling the fluid acted upon bythe piston and wherein the coolant circuit uses the same fluid to coolthe linear motor and to recool the fluid acted upon by the piston. 28.Fluid machine as claimed in claim 17, wherein the piston is a liquidpiston for compressing gases to high pressures and wherein the liquidpiston is formed of a magnetizable liquid which does not have a vaporpressure that will cause molecules of the liquid to mix with the gas tobe compressed.
 29. Fluid machine as claimed in claim 28, wherein theliquid is an ionic liquid.
 30. Fluid machine as claimed in claim 28,wherein the split pipe is located within the coil in a radial directionso that the split pipe surrounds the liquid.
 31. Fluid machine asclaimed in claim 28, wherein at least one heat exchanger is provided forre-cooling the liquid.
 32. Fluid machine as claimed in claim 28, whereinthe liquid also cools the linear motor.
 33. Fluid machine as claimed inclaim 27, wherein the at least one cylinder comprises two cylinders, andwherein the linear motor and the split pipe are located between the twocylinders.
 34. Fluid machine as claimed in claim 27, wherein the splitpipe is made of one of a metal, a plastic and a ceramic.
 35. Fluidmachine as claimed in claim 17, wherein the at least one cylindercomprises two cylinders, and wherein the linear motor and the split pipeare located between the two cylinders.
 36. Fluid machine as claimed inclaim 17, wherein the split pipe is made of one of a metal, a plasticand a ceramic.